The present invention relates generally to a method for analyzing a first signal indicative of a property of an electrical utility power system, and more particularly to a method for compensating for phase drift of the first signal relative to a second signal.
Generally, electrical power originates at a generation station and is transmitted to customers by a system of conductors and other equipment that make up an electrical power system. In a typical prior art power system, an analog signal indicative of a property of electrical power is monitored to determine whether the power system is operating properly. In this regard, the monitored signal is discretely sampled and a plurality of data points are generated that together digitally represent the monitored signal. Data points are grouped together into sets representing a cycle or number of cycles of the periodic property for analysis. Each data point is associated with a particular position during a cycle. The position of a data point within a cycle can be identified in the frequency domain by phase angle.
To monitor the operation of the power system, the set of data points representing the sampled signal is compared to a set of data points that represents a baseline signal. When the sampled signal and the baseline signal are compared, individual data points from corresponding positions during a cycle are compared. If the two data points are from the same position in the cycle, a difference in the magnitude of the data points can be attributed to the operation of the power system. However, if the two data points are not from the same position in their respective cycles, a portion of the difference in magnitude may be attributed to their relative positions in the cycle. In other words, if sampling errors cause a data point to relate to a different position in the cycle than the data point to which it is intended to be compared, then differences in the data points can reflect the sampling errors and not the operation of the power system. Such results can be misleading.
One cause of sampled data points being out of position relative to baseline data points is phase drift. As used herein and discussed below, the term “phase drift” indicates that the digital representations of the two signals differ in phase to some degree.